Mollicutes is a class of bacteria[2] distinguished by the absence of a cell wall. The word "Mollicutes" is derived from the Latin mollis (meaning "soft" or "pliable"), and cutis (meaning "skin"). Individuals are very small, typically only 0.2–0.3 μm (200-300 nm) in size and have a very small genome size. They vary in form, although most have sterols that make the cell membrane somewhat more rigid. Many are able to move about through gliding, but members of the genus Spiroplasma are helical and move by twisting. The best-known genus in the Mollicutes is Mycoplasma.

Mollicutes are parasites of various animals and plants, living on or in the host's cells. Many cause diseases in humans, attaching to cells in the respiratory or urogenital tracts, particularly species of Mycoplasma and Ureaplasma. Phytoplasma and Spiroplasma are plant pathogens associated with insect vectors.

Whereas formerly the trivial name "mycoplasma" has commonly denoted any member of the class Mollicutes, it now refers exclusively to a member of the genus Mycoplasma.

Analysis of the genomes of mycoplasmas gives solid support for the hypothesis that mycoplasmas have developed from Gram-positive bacteria by a process of reductive evolution. By adopting a parasitic mode of life with use of nutrients from their hosts, mycoplasmas were able to reduce their genetic material considerably. On the other hand, mycoplasma lost the genes for many assimilative processes. Thus, Mycoplasma possibly became the smallest self-replicating organism in nature. Mycoplasma genitalium, with 580,000 base pairs, has an especially small genome size. Some phytoplasmas also have a very small genome size. The genera with the smallest genome are considered to be phylogenetically the most "recent" mollicutes.

To maintain their parasitic mode of life the mollicutes have developed rather sophisticated mechanisms to colonize their hosts and resist the host immune system.[3]

The classification of the Mollicutes has always been difficult. The individuals are tiny, and being parasites, they have to be cultivated on special media. Until now, many species could not be isolated at all. In the beginning, whether they were fungi, viruses, or bacteria was not clear. Also, the resemblance to L-forms was confusing. At first, all members of the class Mollicutes were generally named "mycoplasma" or pleuropneumonia-like organism (PPLO). Mollicutes other than some members of genus Mycoplasma were still unidentified. The first species of Mycoplasma/Mollicutes, that could be isolated was Mycoplasma mycoides. This bacterium was cultivated by Nocard and Roux in 1898.[4]

In 1956, D.G. Edward and E.A. Freundt made a first proposal for classifying and naming PPLOs. They left undecided, however, whether they belong to the bacteria (prokaryotes, in 1956 called "Schizomycetes") or to the eukaryotes. As type species (name-giving species) of the PPLOs/mycoplasmas, Edward and Freundt proposed Mycoplasma mycoides, being the causative organism of bovine pleuropneumonia and referring to the pleuropneumonia-like organisms. Until then, Mycoplasma mycoides was known as Asterococcus mycoides, but later that name was not recognized as valid. In their publication of 1956, they described 15 species of Mycoplasma.[5] In 1967 the class Mollicutes, containing the order Mycoplasmatales, was proposed by the Subcommittee on Taxonomy of the Mycoplasmata.[1] Now, the name Mycoplasma should exclusively be used for members of the genusMycoplasma, rather than the use as a trivial name for any mollicute. As the trivial name has been used in literature for a long time, this is yet not always the case.

Phylogenetic position of Mollicutes among bacteria, using 16S rRNA sequences.[7]

For classification and nomenclature of Mollicutes, there are special rules, which are maintained by the International Committee on Systematics of Prokaryotes (ICSP) Subcommittee on the Taxonomy of Mollicutes (formerly the International Committee on Systematic Bacteriology (ICSB) Subcommittee on taxonomy of Mycoplasmatales).[8]

The results of Mollicutes phylogenetic analyses have been controversial. Some taxonomists place them in Firmicutes, others in Tenericutes. Woese et al. suggested that the Mollicutes might have been derived from different branches of bacteria. They concluded, that the Mollicutes are not a phylogenetically coherent group and therefore do not form a distinct higher level taxon. Instead, they cluster within Gram-positive bacteria of the phylum Firmicutes.[10] The results of molecular phylogenetic analyses have partly depend on the chosen molecular marker, like rRNA, elongation factor or another protein.[11] Phylogenetic trees based on phosphoglycerate kinase (Pgk) amino acid sequences' indicated a monophyletic origin for the Mollicutes within the Firmicutes.[12]

An early edition of Bergey’s Manual of Systematic Bacteriology placed class Mollicutes within phylum Firmicutes,[13][14] whereas in the announced 2nd edition, they are moved to a separate phylum Tenericutes.[15][16][17] The change is motivated by "their unique phenotypic properties, in particular the lack of rigid cell walls, and the general low support by alternative markers".[11] In the Taxonomic Outline of Bacteria and Archaea (TOBA Release 7.7), March 2007, the Mollicutes are a class in the phylum Firmicutes.[18]

1.
Taxonomy (biology)
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Taxonomy is the science of defining groups of biological organisms on the basis of shared characteristics and giving names to those groups. The exact definition of taxonomy varies from source to source, but the core of the remains, the conception, naming. There is some disagreement as to whether biological nomenclature is considered a part of taxonomy, the broadest meaning of taxonomy is used here. The word taxonomy was introduced in 1813 by Candolle, in his Théorie élémentaire de la botanique, the term alpha taxonomy is primarily used today to refer to the discipline of finding, describing, and naming taxa, particularly species. In earlier literature, the term had a different meaning, referring to morphological taxonomy, ideals can, it may be said, never be completely realized. They have, however, a value of acting as permanent stimulants. Some of us please ourselves by thinking we are now groping in a beta taxonomy, turrill thus explicitly excludes from alpha taxonomy various areas of study that he includes within taxonomy as a whole, such as ecology, physiology, genetics, and cytology. He further excludes phylogenetic reconstruction from alpha taxonomy, thus, Ernst Mayr in 1968 defined beta taxonomy as the classification of ranks higher than species. This activity is what the term denotes, it is also referred to as beta taxonomy. How species should be defined in a group of organisms gives rise to practical and theoretical problems that are referred to as the species problem. The scientific work of deciding how to define species has been called microtaxonomy, by extension, macrotaxonomy is the study of groups at higher taxonomic ranks, from subgenus and above only, than species. While some descriptions of taxonomic history attempt to date taxonomy to ancient civilizations, earlier works were primarily descriptive, and focused on plants that were useful in agriculture or medicine. There are a number of stages in scientific thinking. Early taxonomy was based on criteria, the so-called artificial systems. Later came systems based on a complete consideration of the characteristics of taxa, referred to as natural systems, such as those of de Jussieu, de Candolle and Bentham. The publication of Charles Darwins Origin of Species led to new ways of thinking about classification based on evolutionary relationships and this was the concept of phyletic systems, from 1883 onwards. This approach was typified by those of Eichler and Engler, the advent of molecular genetics and statistical methodology allowed the creation of the modern era of phylogenetic systems based on cladistics, rather than morphology alone. Taxonomy has been called the worlds oldest profession, and naming and classifying our surroundings has likely been taking place as long as mankind has been able to communicate

2.
Bacteria
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Bacteria constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a number of shapes, ranging from spheres to rods, Bacteria were among the first life forms to appear on Earth, and are present in most of its habitats. Bacteria inhabit soil, water, acidic hot springs, radioactive waste, Bacteria also live in symbiotic and parasitic relationships with plants and animals. Most bacteria have not been characterised, and only half of the bacterial phyla have species that can be grown in the laboratory. The study of bacteria is known as bacteriology, a branch of microbiology, There are typically 40 million bacterial cells in a gram of soil and a million bacterial cells in a millilitre of fresh water. There are approximately 5×1030 bacteria on Earth, forming a biomass which exceeds that of all plants, Bacteria are vital in many stages of the nutrient cycle by recycling nutrients such as the fixation of nitrogen from the atmosphere. The nutrient cycle includes the decomposition of bodies and bacteria are responsible for the putrefaction stage in this process. In March 2013, data reported by researchers in October 2012, was published and it was suggested that bacteria thrive in the Mariana Trench, which with a depth of up to 11 kilometres is the deepest known part of the oceans. Other researchers reported related studies that microbes thrive inside rocks up to 580 metres below the sea floor under 2.6 kilometres of ocean off the coast of the northwestern United States. According to one of the researchers, You can find microbes everywhere—theyre extremely adaptable to conditions, the vast majority of the bacteria in the body are rendered harmless by the protective effects of the immune system, though many are beneficial particularly in the gut flora. However several species of bacteria are pathogenic and cause diseases, including cholera, syphilis, anthrax, leprosy. The most common fatal diseases are respiratory infections, with tuberculosis alone killing about 2 million people per year. In developed countries, antibiotics are used to treat infections and are also used in farming, making antibiotic resistance a growing problem. Once regarded as constituting the class Schizomycetes, bacteria are now classified as prokaryotes. Unlike cells of animals and other eukaryotes, bacterial cells do not contain a nucleus and these evolutionary domains are called Bacteria and Archaea. The ancestors of modern bacteria were unicellular microorganisms that were the first forms of life to appear on Earth, for about 3 billion years, most organisms were microscopic, and bacteria and archaea were the dominant forms of life. In 2008, fossils of macroorganisms were discovered and named as the Francevillian biota, however, gene sequences can be used to reconstruct the bacterial phylogeny, and these studies indicate that bacteria diverged first from the archaeal/eukaryotic lineage. Bacteria were also involved in the second great evolutionary divergence, that of the archaea, here, eukaryotes resulted from the entering of ancient bacteria into endosymbiotic associations with the ancestors of eukaryotic cells, which were themselves possibly related to the Archaea

3.
Micrometer
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Micrometers are usually, but not always, in the form of calipers, which is why micrometer caliper is another common name. The spindle is a very accurately machined screw and the object to be measured is placed between the spindle and the anvil, the spindle is moved by turning the ratchet knob or thimble until the object to be measured is lightly touched by both the spindle and the anvil. Micrometers are also used in telescopes or microscopes to measure the apparent diameter of celestial bodies or microscopic objects, the micrometer used with a telescope was invented about 1638 by William Gascoigne, an English astronomer. Colloquially the word micrometer is often shortened to mike or mic, the word micrometer is a neoclassical coinage from Greek micros, meaning small, and metron, meaning measure. The Merriam-Webster Collegiate Dictionary says that English got it from French, neither the metre nor the micrometre nor the micrometer as we know them today existed at that time. However, the people of that time did have much need for, and interest in, the word was no doubt coined in reference to this endeavor, even if it did not refer specifically to its present-day senses. In 1844 details of Whitworths workshop micrometer were published and this was described as having a strong frame of cast iron, the opposite ends of which were two highly finished steel cylinders, which traversed longitudinally by action of screws. The ends of the cylinders where they met was of hemispherical shape, one screw was fitted with a wheel graduated to measure to the ten thousandth of an inch. His object was to furnish ordinary mechanics with an instrument which, the micrometer caliper was introduced to the mass market in anglophone countries by Brown & Sharpe in 1867, allowing the penetration of the instruments use into the average machine shop. Brown & Sharpe were inspired by earlier devices, one of them being Palmers design. In 1888 Edward W. Morley added to the precision of micrometric measurements, each type of micrometer caliper can be fitted with specialized anvils and spindle tips for particular measuring tasks. For example, the anvil may be shaped in the form of a segment of screw thread, in the form of a v-block, universal micrometer sets come with interchangeable anvils, such as flat, spherical, spline, disk, blade, point, and knife-edge. The term universal micrometer may also refer to a type of micrometer whose frame has modular components, allowing one micrometer to function as outside mic, depth mic, step mic, blade micrometers have a matching set of narrow tips. They allow, for example, the measuring of a narrow o-ring groove, pitch-diameter micrometers have a matching set of thread-shaped tips for measuring the pitch diameter of screw threads. Limit mics have two anvils and two spindles, and are used like a snap gauge, the part being checked must pass through the first gap and must stop at the second gap in order to be within specification. The two gaps accurately reflect the top and bottom of the tolerance range, bore micrometer, typically a three-anvil head on a micrometer base used to accurately measure inside diameters. Tube micrometers have a cylindrical anvil positioned perpendicularly to a spindle and is used to measure the thickness of tubes. Micrometer stops are micrometer heads that are mounted on the table of a milling machine, bedways of a lathe, or other machine tool

4.
Phytoplasma
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Phytoplasmas are obligate bacterial parasites of plant phloem tissue and of the insect vectors that are involved in their plant-to-plant transmission. Phytoplasmas were discovered in 1967 by Japanese scientists who termed them mycoplasma-like organisms or MLOs, since their discovery, phytoplasmas have resisted all attempts at in vitro culture in any cell-free medium, routine cultivation in an artificial medium thus remains a major challenge. Although phytoplasmas have recently reported to be grown in a specific artificial medium. Phytoplasmas are characterized by the lack of a wall, a pleiomorphic or filamentous shape, a diameter normally less than 1 μm. Phytoplasmas are pathogens of important plants, including coconut, sugarcane. Phytoplasmas are most prevalent in tropical and subtropical regions and they are transmitted from plant to plant by vectors in which they both survive and replicate. Viral and phytoplasmic infections share some symptoms, Phytoplasmas are Mollicutes, which are bound by a triple-layered membrane, rather than a cell wall. The phytoplasma cell membranes studied to date usually contain a single immunodominant protein of unknown function that constitutes most of the protein in the membrane, a typical phytoplasma is pleiomorphic or filamentous in shape and is less than 1 μm in diameter. Like other prokaryotes, phytoplasmic DNA is distributed throughout the cytoplasm, Phytoplasmas can infect and cause various symptoms in more than 700 plant species. One characteristic symptom is abnormal floral organ development including phyllody, phytoplasma-harboring flowering plants may nevertheless be sterile. The expression of genes involved in maintaining the apical meristem or in the development of organs is altered in the morphologically affected floral organs of phytoplasma-infected plants. These symptoms may be attributable to stress caused by the rather than a specific pathogenetic process. Many phytoplasma-infected plants develop a bushy or witches broom appearance due to changes in their growth patterns. Most plants exhibit apical dominance but infection can trigger the proliferation of auxiliary shoots, such symptoms are actually useful in the commercial production of poinsettias. Infection triggers more axillary shoot production, the plants thus produce more than a single flower. Many plant pathogens produce virulence factors that modulate or interfere with normal host processes to the benefit of the pathogens. In 2009, a protein, termed “tengu-su inducer”, was identified from a phytoplasma causing yellowing of onions. TENGU induces characteristic symptoms, including witches’ broom and dwarfism, transgenic expression of TENGU in Arabidopsis plants induced sterility in male and female flowers

5.
Trivial name
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In chemistry, a trivial name is a nonsystematic name for a chemical substance. That is, the name is not recognized according to the rules of any system of chemical nomenclature such as IUPAC inorganic or IUPAC organic nomenclature. A trivial name is not a name and is usually a common name. Generally, trivial names are not useful in describing the properties of the thing being named. Properties such as the structure of a chemical compound are not indicated. And, in cases, trivial names can be ambiguous or will carry different meanings in different industries or in different geographic regions. On the other hand, systematic names can be so convoluted, as a result, a limited number of trivial chemical names are retained names, an accepted part of the nomenclature. Trivial names often arise in the language, they may come from historic usages in, for example. Many trivial names pre-date the institution of formal naming conventions, all elements that have been isolated have trivial names. In scientific documents, international treaties, patents and legal definitions and this need is satisfied by systematic names. One such system, established by the International Union of Pure, other systems have been developed by the American Chemical Society, the International Organization for Standardization, and the World Health Organization. However, chemists still use names that are not systematic because they are traditional or because they are more convenient than the systematic names. The word trivial, often used in a sense, was intended to mean commonplace. In addition to names, chemists have constructed semi-trivial names by appending a standard symbol to a trivial stem. Some trivial and semi-trivial names are so used that they have been officially adopted by IUPAC. Traditional names of elements are trivial, some originating in alchemy, IUPAC has accepted these names, but has also defined systematic names of elements that have not yet been prepared. It has adopted a procedure by which the scientists who are credited with preparing an element can propose a new name, once the IUPAC has accepted such a name, it replaces the systematic name. Nine elements were known by the Middle Ages – gold, silver, tin, mercury, copper, lead, iron, sulfur, and carbon

6.
Eukaryote
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A eukaryote is any organism whose cells contain a nucleus and other organelles enclosed within membranes. Eukaryotes belong to the taxon Eukarya or Eukaryota, the presence of a nucleus gives eukaryotes their name, which comes from the Greek εὖ and κάρυον. Eukaryotic cells also contain other membrane-bound organelles such as mitochondria and the Golgi apparatus, in addition, plants and algae contain chloroplasts. Eukaryotic organisms may be unicellular or multicellular, only eukaryotes form multicellular organisms consisting of many kinds of tissue made up of different cell types. Eukaryotes can reproduce asexually through mitosis and sexually through meiosis and gamete fusion. In mitosis, one cell divides to produce two identical cells. In meiosis, DNA replication is followed by two rounds of division to produce four daughter cells each with half the number of chromosomes as the original parent cell. These act as sex cells resulting from genetic recombination during meiosis, the domain Eukaryota appears to be monophyletic, and so makes up one of the three domains of life. The two other domains, Bacteria and Archaea, are prokaryotes and have none of the above features, eukaryotes represent a tiny minority of all living things. However, due to their larger size, eukaryotes collective worldwide biomass is estimated at about equal to that of prokaryotes. Eukaryotes first developed approximately 1. 6–2.1 billion years ago, in 1905 and 1910, the Russian biologist Konstantin Mereschkowsky argued three things about the origin of nucleated cells. Firstly, plastids were reduced cyanobacteria in a symbiosis with a non-photosynthetic host, secondly, the host had earlier in evolution formed by symbiosis between an amoeba-like host and a bacteria-like cell that formed the nucleus. Thirdly, plants inherited photosynthesis from cyanobacteria, the split between the prokaryotes and eukaryotes was introduced in the 1960s. The concept of the eukaryote has been attributed to the French biologist Edouard Chatton, the terms prokaryote and eukaryote were more definitively reintroduced by the Canadian microbiologist Roger Stanier and the Dutch-American microbiologist C. B. van Niel in 1962. In his 1938 work Titres et Travaux Scientifiques, Chatton had proposed the two terms, calling the bacteria prokaryotes and organisms with nuclei in their cells eukaryotes. However he mentioned this in one paragraph, and the idea was effectively ignored until Chattons statement was rediscovered by Stanier. In 1967, Lynn Margulis provided microbiological evidence for endosymbiosis as the origin of chloroplasts and mitochondria in cells in her paper. In the 1970s, Carl Woese explored microbial phylogenetics, studying variations in 16S ribosomal RNA and this helped to uncover the origin of the eukaryotes and the symbiogenesis of two important eukaryote organelles, mitochondria and chloroplasts

7.
Phosphoglycerate kinase
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Phosphoglycerate kinase is an enzyme that catalyzes the reversible transfer of a phosphate group from 1, 3-bisphosphoglycerate to ADP producing 3-phosphoglycerate and ATP. Like all kinases it is a transferase, PGK is a major enzyme used in glycolysis, in the first ATP-generating step of the glycolytic pathway. In gluconeogenesis, the reaction catalyzed by PGK proceeds in the direction, generating ADP and 1. In humans, two isozymes of PGK have been so far identified, PGK1 and PGK2, PGK is present in all living organisms as one of the two ATP-generating enzymes in glycolysis. In the gluconeogenic pathway, PGK catalyzes the reverse reaction, under biochemical standard conditions, the glycolytic direction is favored. In the Calvin cycle in photosynthetic organisms, PGK catalyzes the phosphorylation of 3-PG, producing 1, 3-BPG and ADP, as part of the reactions that regenerate ribulose-1, 5-bisphosphate. PGK has been reported to exhibit thiol reductase activity on plasmin, leading to angiostatin formation, the enzyme was also shown to participate in DNA replication and repair in mammal cell nuclei. The human isozyme PGK2, which is expressed during spermatogenesis, was shown to be essential for sperm function in mice. Click on genes, proteins and metabolites below to link to respective articles, PGK is found in all living organisms and its sequence has been highly conserved throughout evolution. The enzyme exists as a 415-residue monomer containing two nearly equal-sized domains that correspond to the N- and C-termini of the protein, 3-phosphoglycerate binds to the N-terminal, while the nucleotide substrates, MgATP or MgADP, bind to the C-terminal domain of the enzyme. This extended two-domain structure is associated with large-scale hinge-bending conformational changes, the two domains of the protein are separated by a cleft and linked by two alpha-helices. At the core of each domain is a 6-stranded parallel beta-sheet surrounded by alpha helices, the two lobes are capable of folding independently, consistent with the presence of intermediates on the folding pathway with a single domain folded. Though the binding of either substrate triggers a change, only through the binding of both substrates does domain closure occur, leading to the transfer of the phosphate group. Magnesium ions are complexed to the phosphate groups the nucleotide substrates of PGK. It is known that in the absence of magnesium, no enzyme activity occurs and it is theorized that the ion may also encourage domain closure when PGK has bound both substrates. Without either substrate bound, PGK exists in an open conformation, then, in the case of the forward glycolytic reaction, the beta-phosphate of ADP initiates a nucleophilic attack on the 1-phosphate of 1, 3-BPG. The Lys219 on the enzyme guides the group to the substrate. In the glycolytic pathyway,1, 3-BPG is the donor and has a high phosphoryl-transfer potential

8.
Phenotype
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A phenotype is the composite of an organisms observable characteristics or traits, such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior. A phenotype results from the expression of a genetic code, its genotype, as well as the influence of environmental factors. When two or more clearly different phenotypes exist in the population of a species, the species is called polymorphic. A well-documented polymorphism is Labrador Retriever coloring, while the color depends on many genes, it is clearly seen in the environment as yellow, black. This genotype-phenotype distinction was proposed by Wilhelm Johannsen in 1911 to make clear the difference between an organisms heredity and what that heredity produces, the distinction is similar to that proposed by August Weismann, who distinguished between germ plasm and somatic cells. The term phenotype has sometimes incorrectly used as a shorthand for phenotypic difference from wild type. Despite its seemingly straightforward definition, the concept of the phenotype has hidden subtleties and it may seem that anything dependent on the genotype is a phenotype, including molecules such as RNA and proteins. It may seem that this goes beyond the intentions of the concept with its focus on the organism in itself. Either way, the term phenotype includes traits or characteristics that can be visible by some technical procedure. A notable extension to this idea is the presence of molecules or metabolites that are generated by organisms from chemical reactions of enzymes. Another extension adds behavior to the phenotype, since behaviors are also observable characteristics, behavioral phenotypes include cognitive, personality, and behavioral patterns. Some behavioral phenotypes may characterize psychiatric disorders or syndromes, phenotypic variation is a fundamental prerequisite for evolution by natural selection. It is the organism as a whole that contributes to the next generation. Without phenotypic variation, there would be no evolution by natural selection, the plant Hieracium umbellatum is found growing in two different habitats in Sweden. These habitats alternate along the coast of Sweden and the habitat that the seeds of Hieracium umbellatum land in, the concept of phenotype can be extended to variations below the level of the gene that affect an organisms fitness. For example, silent mutations that do not change the amino acid sequence of a gene may change the frequency of guanine-cytosine base pairs. The term extended phenotype refers to the idea that a phenotype is not restricted to biological processes, the concept generalized by Richard Dawkins explains that phenotype includes all the influence a gene has on the environment and other organisms. ”There are three types of extended phenotypes. The first describes an organism using architectural constructions to modify their environment for living, the most common example given by Dawkins is the beaver

9.
L-form bacteria
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L-form bacteria, also known as L-phase bacteria, L-phase variants, and cell wall-deficient bacteria, are strains of bacteria that lack cell walls. They were first isolated in 1935 by Emmy Klieneberger-Nobel, who named them L-forms after the Lister Institute in London where she was working. Some parasitic species of bacteria, such as mycoplasma, also lack a cell wall, bacterial morphology is determined by the cell wall. Since the L-form has no wall, its morphology is different from that of the strain of bacteria from which it is derived. Typical L-form cells are spheres or spheroids, for example, L-forms of the rod-shaped bacterium Bacillus subtilis appear round when viewed by phase contrast microscopy or by transmission electron microscopy. Although L-forms can develop from Gram-positive as well as from Gram-negative bacteria, in a Gram stain test, the cell wall is important for cell division, which, in most bacteria, occurs by binary fission. This process usually requires a wall and components of the bacterial cytoskeleton such as FtsZ. The ability of L-form bacteria to grow and divide in the absence of both of these structures is highly unusual, and may represent a form of division that was important in early forms of life. This novel mode of division seems to involve the extension of thin protrusions from the cells surface, the lack of cell wall in L-forms means that division is disorganised, giving rise to a variety of cell sizes, from very tiny to very big. L-forms can be generated in the laboratory from many species that usually have cell walls. This is done by inhibiting peptidoglycan synthesis with antibiotics or treating the cells with lysozyme, the L-forms are generated in a culture medium that is the same osmolarity as the bacterial cytosol, which prevents cell lysis by osmotic shock. Some studies have identified mutations that occur, as these strains are derived from normal bacteria, one such point mutation is in an enzyme involved in the mevalonate pathway of lipid metabolism that increased the frequency of L-form formation 1, 000-fold. The reason for this effect is not known, but it is presumed that the increase is related to this role in making a lipid important in peptidoglycan synthesis. Another methodology of induction relies on nanotechnology and landscape ecology, microfluidics devices can be built in order to challenge peptidoglycan synthesis by extreme spatial confinement. The two extreme viewpoints on this question are that L-form bacteria are either laboratory curiosities of no significance or important. Research on L-form bacteria is continuing, the formation of strains of bacteria lacking cell walls has also been proposed to be important in the acquisition of bacterial antibiotic resistance. L-form bacteria may be useful in research on early forms of life and these strains are being examined for possible uses in biotechnology as host strains for recombinant protein production. Here, the absence of a wall can allow production of large amounts of secreted proteins that would otherwise accumulate in the periplasmic space of bacteria

10.
Microbiological culture
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A microbiological culture, or microbial culture, is a method of multiplying microbial organisms by letting them reproduce in predetermined culture media under controlled laboratory conditions. Microbial cultures are used to determine the type of organism, its abundance in the sample being tested and it is one of the primary diagnostic methods of microbiology and used as a tool to determine the cause of infectious disease by letting the agent multiply in a predetermined medium. Furthermore, the culture is more generally used informally to refer to selectively growing a specific kind of microorganism in the lab. Microbial cultures are foundational and basic methods used extensively as a research tool in molecular biology. It is often essential to isolate a pure culture of microorganisms, a pure culture is a population of cells or multicellular organisms growing in the absence of other species or types. A pure culture may originate from a cell or single organism. For the purpose of gelling the microbial culture, the medium of agarose gel is used, agar is a gelatinous substance derived from seaweed. A cheap substitute for agar is guar gum, which can be used for the isolation, there are several types of bacterial culture methods that are selected based on the agent being cultured and the downstream use. One method of culture is liquid culture, in which the desired bacteria are suspended in a liquid nutrient medium, such as Luria Broth. This allows a scientist to grow up large amounts of bacteria for a variety of downstream applications, liquid cultures are ideal for preparation of an antimicrobial assay in which the experimenter inoculates liquid broth with bacteria and lets it grow overnight. Then they would take aliquots of the sample to test for the activity of a specific drug or protein. As an alternative, the microbiologist may decide to use static liquid cultures and these cultures are not shaken and they provide the microbes with an oxygen gradient. Microbiological cultures can be grown in petri dishes of differing sizes that have a layer of agar-based growth medium. Once the growth medium in the dish is inoculated with the desired bacteria. After the desired level of growth is achieved, agar plates can be stored upside down in a refrigerator for a period of time to keep bacteria for future experiments. There are a variety of additives that can be added to agar before it is poured into a plate, some types of bacteria can only grow in the presence of certain additives. This can also be used when creating engineered strains of a bacteria that contain an antibiotic-resistance gene, when the selected antibiotic is added to the agar, only bacterial cells containing the gene insert conferring resistance will be able to grow. This allows the researcher to select only the colonies that were successfully transformed, stab cultures are similar to agar plates, but are formed by solid agar in a test tube

11.
Gram-positive bacteria
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Gram-positive bacteria are bacteria that give a positive result in the Gram stain test. Gram-positive bacteria take up the crystal violet stain used in the test and this is because the thick peptidoglycan layer in the bacterial cell wall retains the stain after it is washed away from the rest of the sample, in the decolorization stage of the test. Their peptidoglycan layer is thinner and sandwiched between an inner cell membrane and a bacterial outer membrane, causing them to take up the counterstain. Despite their thicker peptidoglycan layer, gram-positive bacteria are more receptive to antibiotics than gram-negative, peptidoglycan chains are cross-linked to form rigid cell walls by a bacterial enzyme DD-transpeptidase. A much smaller volume of periplasm than that in gram-negative bacteria, only some species have a capsule usually consisting of polysaccharides. Also only some species are flagellates, and when they do have flagella they only have two basal body rings to support them, both gram-positive and gram-negative bacteria commonly have a surface layer called an S-layer. In gram-positive bacteria, the S-layer is attached to the peptidoglycan layer, specific to gram-positive bacteria is the presence of teichoic acids in the cell wall. Some of these are lipoteichoic acids, which have a component in the cell membrane that can assist in anchoring the peptidoglycan. Along with cell shape, Gram staining is a method used to differentiate bacterial species. Historically, the kingdom Monera was divided into four divisions based primarily on Gram staining, based on molecular studies of the 16S sequences, Woese recognised twelve bacterial phyla. Two of these were both gram-positive and were divided on the proportion of the guanine and cytosine content in their DNA, the high G + C phylum was made up of the Actinobacteria and the low G + C phylum contained the Firmicutes. The Actinobacteria include the Corynebacterium, Mycobacterium, Nocardia and Streptomyces genera, the Firmicutes, have a 45–60% GC content, but this is lower than that of the Actinobacteria. The gram-positive and gram-negative staining response is not a reliable characteristic as these two kinds of bacteria do not form phylogenetic coherent groups. All gram-positive bacteria are bounded by a lipid membrane, and, in general. For the bacterial cells bounded by a cell membrane, the term monoderm bacteria or monoderm prokaryotes has been proposed. The presence of inner and outer cell membranes defines a new compartment in these cells and these bacteria have been designated as diderm bacteria. The distinction between the monoderm and diderm bacteria is supported by conserved signature indels in a number of important proteins, of these two structurally distinct groups of bacteria, monoderms are indicated to be ancestral. In general, gram-positive bacteria are monoderms and have a lipid bilayer whereas gram-negative bacteria are diderms and have two bilayers

12.
Cell wall
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A cell wall is a structural layer surrounding some types of cells, situated outside the cell membrane. It can be tough, flexible, and sometimes rigid and it provides the cell with both structural support and protection, and also acts as a filtering mechanism. Cell walls are present in most prokaryotes, in algae, plants and fungi, a major function is to act as pressure vessels, preventing over-expansion of the cell when water enters. The composition of cell walls varies between species and may depend on type and developmental stage. The primary cell wall of plants is composed of the polysaccharides cellulose, hemicellulose. Often, other such as lignin, suberin or cutin are anchored to or embedded in plant cell walls. Algae possess walls made of glycoproteins and polysaccharides such as carrageenan, in bacteria, the cell wall is composed of peptidoglycan. The cell walls of archaea have various compositions, and may be formed of glycoprotein S-layers, pseudopeptidoglycan, Fungi possess cell walls made of the glucosamine polymer chitin. Unusually, diatoms have a wall composed of biogenic silica. A plant cell wall was first observed and named by Robert Hooke in 1665, in 1804, Karl Rudolphi and J. H. F. Link proved that cells had independent cell walls, before, it had been thought that cells shared walls and that fluid passed between them this way. The mode of formation of the wall was controversial in the 19th century. Hugo von Mohl advocated the idea that the wall grows by apposition. Carl Nägeli believed that the growth of the wall in thickness, each theory was improved in the following decades, the apposition theory by Eduard Strasburger, and the intussusception theory by Julius Wiesner. In 1930, Ernst Münch coined the term apoplast in order to separate the living symplast from the dead plant region, Cell walls serve similar purposes in those organisms that possess them. They may give cells rigidity and strength, offering protection against mechanical stress, in multicellular organisms, they permit the organism to build and hold a definite shape. Cell walls also limit the entry of large molecules that may be toxic to the cell and they further permit the creation of stable osmotic environments by preventing osmotic lysis and helping to retain water. Their composition, properties, and form may change during the cell cycle, in most cells, the cell wall is flexible, meaning that it will bend rather than holding a fixed shape, but has considerable tensile strength

Here the relation between genotype and phenotype is illustrated, using a Punnett square, for the character of petal color in pea plants. The letters B and b represent genes for color, and the pictures show the resultant flowers.